Quantum evolution

Australian researchers report they've made a breakthrough in quantum computing. So how does their discovery fit in the race to build a supercomputer?

By Stephen Pincock

Artist's impression of a phosphorus atom (red sphere surrounded by electron cloud, with arrow showing the spin direction) coupled to a silicon single-electron transistor. (Source: Tony Melov/University of New South Wales)

Standing in a light-filled laboratory at the University of New South Wales, Morello grips a small gold-plated circuit board in his fingertips. Slightly larger than a matchbox, its surface is punctured by a constellation of tiny holes and overlaid with white shapes like raindrops running down a window.

The tails of the raindrops converge near the middle of the golden board, where a tiny opening is waiting for Morello to insert a small piece of specially manipulated silicon.

This sliver of silicon is the same material used to build normal digital computers, but it has been altered at the atomic level.

By replacing selected silicon atoms with atoms of phosphorus, Morello and his colleague Andrew Dzurak have taken a step forward in a global race to build a computer using the weird laws that govern the physical world at the tiniest, quantum, scale.

The dream of building vastly more powerful computers by harnessing quantum properties has been around since the 1970s.

For decades, theorists have filled books and journals with discussion about what such computers could do. But turning those dreams into physical reality has proven a slow process.

Now, using a variety of different technologies, Morello's team and many other scientists around the world are getting closer to building a functioning quantum computer.

There have really been some big strides toward the development of a quantum computer in the last two decades, says Dr Michael Biercuk, a quantum computing researcher at the University of Sydney and a chief investigator in the ARC Centre for Engineered Quantum Systems.

"We keep checking things off that people have said are impossible. Researchers have moved from proof-of-principle demonstrations to working on the engineering challenges we need to overcome to build something useful."

How do quantum computers work?The computer on your desk works by manipulating pieces of information known as binary digits, bits for short. Bits can only have two possible values - either 1 or 0 - normally represented by means of changes in electric current in a circuit.

However in the second half of the 20th century, scientists realised that they could add a twist to this scenario by using special properties of matter that applies when you get down to the sub-atomic scale.

The first of these properties is known as superposition. Put simply, superposition means that physical systems, such as electrons, exist in all their theoretically possible states at once. It's only when you measure them that you get a result that corresponds to just one of the possible states.

Scientists realised that that if they could harness this kind of quantum system, each "quantum bit" of information, or qubit, could actually be both a 0 and 1 simultaneously. As you add more and more bits together, this superposition would allow you to exponentially increase the power of your quantum computer.

The whole idea of quantum computing hinges on the concept of 'entanglement', explains Dr Michelle Simmons, director of the Centre for Quantum Computation and Communication Technology at the University of New South Wales. "It means that if you change the state of one qubit it affects the other qubits that it is entangled with in the system," she says. "It's where the power of quantum computing comes from."

"Entanglement in quantum computing plays the same role as heat in an engine or electricity in a light-bulb," adds Andrew White, a quantum physicist from the University of Queensland. "It's the underlying phenomenon you need to understand to build a quantum computer."

Cracking codes, designing drugs

As theorists thought more about theoretical quantum computers, they came up with specific problems that they would be ideal for solving.

"The thing that really got the thing moving was in 1994 when a computer scientist called Peter Shor came up with a theoretical algorithm that could be run on a quantum computer if it existed," says Dzurak.

Shor's algorithm had the potential to solve a problem at the heart of the systems we use to keep our data secure, called public key encryption. This encryption system relies on the fact that conventional computers struggle to figure out the two large prime numbers that have been multiplied together to form another even more enormous number.

Shor figured out that a quantum computer would be great at solving this problem quickly, explains Dzurak. "All of a sudden one could see an application for quantum computers that was something that a conventional computer simply couldn't do in any useful time."

Not surprisingly, Shor's realisation that quantum computers were ideal code-cracking machines generated interest from governments and the military. Their funding support provided an enormous boost to the field.

Since then, other potential uses have emerged. One example is the designing of the chemical molecules that are at the heart of drugs. Currently, this is a process of trial and error, which is one reason the development of new medicines is currently so costly and time-consuming.

"Ideally what you would like is to design them on a computer," says Morello. "Some of these molecules aren't that big, they may be only 20, 30 atoms, maybe 50 atoms. But this is completely impossible on a conventional computer."

Beyond this, it is fair to say that the number of known situations where a quantum computer will out-perform your iPod is currently small, says Dzurak. "It's a handful at the moment. But a couple of them happen to be quite important applications."

Yet it seems likely that once we have quantum computers to play around with, the number of potential applications will increase dramatically. "In 10 or 20 years I don't think the big impacts from quantum computers will be in cracking codes," says White. "We're finding category after category of problems that will be vastly easier if you had a working quantum computer."

Ion traps and beyond

So much for the theory: when it comes to building an actual quantum computer, scientists have had to overcome some major practical hurdles. Crucially, they have needed to find things to use as qubits that can be isolated from the world around them. Then they needed to develop means of having their qubits interact with each other.

The first experimental demonstrations of qubits emerged in the 1990s using a technology that had been developed for atomic clocks, called ion traps. An ion is an atom (or molecule) that has a positive or negative charge. Scientists found that if they suspended such charged atoms in a vacuum using an electromagnetic field, they could use laser beams to control their internal energy levels and to measure them, allowing them to perform operations on basic quantum states.

Ion traps have led the field of quantum computing since the 1990s, partly because ions in a vacuum are well separated from their environment.

Earlier this year, Dr Michael Biercuk and colleagues from the US and South Africa used an ion trap to build a quantum computer with a layer of 300 beryllium ions with interacting spins acting as qubits.

"The system we have developed has the potential to perform calculations that would require a classical machine larger than the size of the known universe - and it does it all in a diameter of less than a millimetre," says Biercuk.

The computer Biercuk's group built is of a type known as a 'quantum simulator', which uses a well-controlled quantum device to mimic another system that is not understood.

"In our case, we are studying the interactions of spins in the field of quantum magnetism - a key problem that underlies new discoveries in materials science for energy, biology, and medicine," says Biercuk.

Quantum dots and silicon

Silicon: Andrea Morello holds a circuit board that can contain a small piece of specially manipulated silicon
(Source: Stephen Pincock)

Ion traps are not the only systems people are exploring for quantum computers. Other approaches developed or conceived since the late 1990s include using superconductors, photons, diamonds, nuclear magnetic resonance on molecules in solutions and many more.

Rather than trapping an ion in a vacuum, Morelli and Dzurak's team are inserting phosphorus atoms in chips of silicon.

"In a sense the silicon is like a vacuum because we make the silicon very pure so that the only kind of thing that's active are the atoms that we deliberately put there," says Dzurak. The spin of an electron orbiting the phosphorus serves as the qubit.

In 2010, the same group of researchers showed that they could measure the spin of that single phosphorous electron, which was controlling the flow of electrons in a nearby circuit.

Now, in research reported in today's issue of Nature , they have demonstrated the ability to both read and write information on a single electron bound to one phosphorus atom embedded in silicon.

For Dzurak and Morello, the beauty of a silicon system lies in the fact that it's a technology conventional computer manufacturers are comfortable with.

"That's the thing about silicon quantum computing and why we've had so much interest and funding, because we're using the technology that is the platform of a trillion dollar industry today. It will look exactly the same. You'll look at it and it'll look just like a computer chip."

Biercuk says the latest research by the UNSW researchers is a major advance towards realising silicon-based quantum processing and takes us closer to the ideal of an integrated quantum computer.

"A major goal for the research community has been to realise the same quantum-coherent functionality afforded by atomic systems in a scalable, integrated platform. Silicon is a natural choice from this perspective, based on decades of research on large-scale integrated circuits for microprocessors and advanced digital electronics."

"Nonetheless the whole community has a long way to go before a practically useful quantum computer is available," he says.

The future

As things stand, quantum computing is roughly at the place conventional computing was at in the 1950s, says Michelle Simmons, whose team at the University of New South Wales created the world's first functioning single atom transistor.

"The first transistor was built in 1947 and the first integrated circuit came in 1960," she says. "Lots was happening in the 13 years in between, and that's where we are at now with quantum computing. We're trying to integrate all the components in the one chip, so to speak."

For a quantum computer to do some calculations that are beyond a conventional computer, researchers estimate it would need to have somewhere in the region of 30 or so qubits operating together. For more powerful operations, hundreds of thousands of qubits are needed. By this standard, Dzurak and Morello's team, and most other research groups, have some way to go.

For now, it's too early to say whether any of the various models of quantum computer might eventually win the race. Many researchers think some combination of different approaches might be most useful.

"We're not quite at the point of selecting between different systems," says University of Queensland physicist Andrew White. "We really don't know what a real quantum computer will look like in the future."

Comments (39)

Comments for this story are now closed. If you would like to have your say on this story, please email ABC Science

Pennpenn :

20 Sep 2012 10:43:53am

I do like this kind of science, manipulating the world at a fundamental level. It's cool that we've got some ideas of how to use such a system, but I feel that this is something we won't discover the true value of until we start using it.

Brian :

20 Sep 2012 7:27:22pm

MY ONE HOPE IS THAT WHEN THIS TECHNOLOGY IS FULLY DEVELOPED AND IS USABLE, THAT IT DOESN'T GO OVERSEAS LIKE MOST OUR EARLIER FANTASTIC INVENTIONS AND THAT THE ORIGINAL PROTOTYPE DOESN'T SIT IN A MUSEUM NEXT TO THE FIRST BLACK BOX FLIGHT RECORDER (AN AUSTRALIAN INVENTION THAT WAS DISMISSED BY THE THEN AVIATION BUREACRACY)

Tony :

22 Sep 2012 7:22:24pm

couldn't agree with you more Brian. This is a fantastic concept and a strong advancement into the future. Australia has been at the forefront of pioneering many significant inventions and changes to world as we know it today. It is about time the australian government fully recognise the advancements our scientists are making today and support them in every possible way. Keeping the inventions within our country and advancing it globaly from australia to the marketable world can only prosper and enhance our economic future and make us a forerunner in the future generations

zara :

Chris :

08 Oct 2012 12:33:27am

The effort to build Quantum Computers has been a global effort... certainly Australia has contributed but not nearly so much as for example the U.S. Defense Program; not that it matters, the point is to build one not to take credit for it. Besides, we're a long way from anyone needing taking credit for building a working quantum computer. Finally, the black box recorder, while useful, is on a completely different order than Quantum Computing, which if invented would affect almost every sector of the market.

I think I think :

13 Oct 2012 10:35:47am

I don't think that is a good argument, especially when this article identifies industry funding that has underpinned research in the field. There is no doubt credit for this technology will be co-opted solely by the major chip manufacturers, who will develop the technology for their personal profit.

It is certain that Australia will not receive a proportionate level of reward from the fruits of this labour as those major companies, no matter how fractional our contribution was.

Help101 :

20 Sep 2012 11:00:27am

Utterly breath taking research and development.

The new knowledge we will be able to obtain from "The system we have developed has the potential to perform calculations that would require a classical machine larger than the size of the known universe - and it does it all in a diameter of less than a millimetre" will potentially be beyond our current imaginations at this point in time.

GerCon :

Blzbob :

20 Sep 2012 4:28:52pm

Makes me think of Douglas Adam's infinite improbability drive, all they had to do to make it was work out just how improbable it actually was (obviously infinitely improbable, which would make it impossible).

Then there is that thing about the God, that whenever man gets close to understanding it, it changes so as to keep him eternally ignorant.

ACR :

20 Sep 2012 4:35:56pm

Certainly amazing.The cynical side of me wonders how soon these will be used as robot traders in the world's stock exchanges. If it happens, is there no danger that something so powerful could quickly get beyond the control of its designers and minders?

anonymousem :

"This sliver of silicon is the same material used to build normal digital computers, but it has been altered at the atomic level. "

Well, yes, so has the silicon in my digital wrist watch.

"By replacing selected silicon atoms with atoms of phosphorus..."

You mean, exactly like the silicon in my digital wrist watch?..

I can learn more by googling for "transmutation doping" and get a more accurate, more up to date and more informative information set than this horseradish you try to pass as information.

ABC. This topic is INCREDIBLE, it's fantastic, it's astounding, it's marvelous... yet the reporting is as if it's been researched by a 15 year old and is writing a highschool report for grade 7.

We figured out how to dope silicon with phosphorus DECADES ago. Pincock is espousing this relatively ancient and well-understood process as if it's akin to tearing holes in spacetime. It's not. ANSTO does it every day - even before its upgrade.

Now, how about you tell us *really* why this stuff is amazing, and stop treating us like fools?

MomentofForce :

21 Sep 2012 12:32:00am

It would also be amazing if researchers would put their egos and IP concerns aside and actually work together on a project like this instead of being in a constant race against each other. But still this stuff is pretty amazing.

Rob :

21 Sep 2012 10:27:47pm

What I've been looking for in these articles is how they overcome the inherent uncertainty at the quantum level. I always thought it would be quantum effects that would limit the ability of conventional computers to get smaller and smaller.Yes, doping silicon with phosphorus is how you build a diode. That is quite conventional.How do you address the different binary states to the same qbit and know which is which? And what if they both need to be 1 (11 instead of 10)? From my understanding at the moment its a bit like you can paint the same wall black and white at the same time, see both colours and know which was the first colour and which was the second...I've read QED by Feynman and get that but I don't understand the concept of quantum computing. Oh well.

Stuart :

24 Sep 2012 5:19:12pm

Quite a lot of the possible computational power comes from harnessing the spin direction rather than the amount of electrons on a wire (potential).

So for example, if you could represent 1's and 0's as up and down qbits then suddenly you can compute trillions of times the speed. Especially if you can get quantum interactions to perform some logic. All this and more with no heat.

I think I think :

"Another possibility is data buses that use entanglement to transfer data rather than electronic pathways, moving information faster than light"

No. It is not possible to transmit information faster than the speed of light using quantum entanglement.

To Rob, there are different methods for inducing the various quantum states required. The qubits must be isolated from environmental disturbance as much as possible, to reduce the chance of undesired quantum decoherence. If this is successful, they can set the state and know that it will remain that way for a period of time with a high level of confidence, and from there they can perform transformations and measurements with confidence.

When a qubit is in a state of superposition, it is both 1 and 0 at the same time. You don't apply one then the other. You can't see it as both a 0 and 1, because as soon as you measure it it will collapse into one state or the other. Sometimes it will be a 1, sometimes it will be a 0.

When you repeat the process, the ratio of 1's to 0's that you measure will be determined by the probability that the qubit should be either a 1 or a 0.

So in a single qubit system, that probability will be roughly 50%. But as you increase the number of entangled qubits the number of viable superposed states increases. So in you analogy, your wall might be black or it might be white when you look at it, depending on the total probability of all the walls in the building being either black or white.

Even that is not a very accurate explanation, but it should set you in the right direction if you want to look into it more yourself.

Fabrice :

21 Sep 2012 11:28:06pm

This article is aimed at normally intelligent and erudit people. Quantum mechanics is incredibly complex and mind boggling and would take more than an article ( to say the least) to even remotely convey, let alone explain, its complexity. I would suggest you read a few books on the subject before you offer an opinion on the worth of this achievement.

jim :

22 Sep 2012 5:10:48am

So, if other metal etc based electrons could be placed and held in silicon etc to excite each other we could play with perpetual motion and on a hyperactive level.Messages and computing could be coiled.A preset panel could decide insulin or heart etc requirements and in medicine,react to problems put to in variances.The perpetual motion, self powering aspect is where artificial intelligence lives.Between poles.Thinking of humans and how we are governed politically , I find that terrifying.The military and security applications are mind boggling. Skynet. Entrapment.Medically,people will walk again, blind will see.Organs replaced.A human could be fitted with a set of strap on flapping wings to fly like a bird. Coordinated public transport. Coordinated everything.1984.